The present invention relates to a trunnion linkage structure for a toroidal continuously variable transmission (CVT), especially, a dual-cavity toroidal CVT, which serves for enhancing efficiency of an assembly operation of the toroidal CVT, and a method of assembling the trunnion linkage structure.
Generally, toroidal CVTs have input and output disks arranged to be rotatable about a common rotation axis, and a plurality of power rollers interposed between the input and output disks in contact therewith via a working fluid (traction oil). Each of the power rollers is supported on a trunnion so as to rotate about a rotation axis and pivotally move about a pivot axis (trunnion axis) perpendicular to the rotation axis thereof. Upon operating the toroidal CVTs, the power rollers are pressed between the input and output disks by applying thereto a load corresponding to a transmission torque. A shear force of the working fluid is caused corresponding to the pressing force applied to the power rollers. Owing to the shear force, the power rollers transmit power between the input and output disks. The power rollers, therefore, tend to be pushed out from a toroidal cavity formed between the input and output disks. In order to avoid the push-out of the power rollers from the toroidal cavity, upper and lower end portions of the trunnion with the power rollers are connected to those of the adjacent trunnion via upper and lower links, respectively. Upon the speed change operation of the toroidal CVT, the respective trunnions are driven by a servo piston to synchronously displace or offset from the non-speed change position where the rotation axes of the power rollers are perpendicular to the common rotation axis of the input and output disks, along a direction of the pivot axis of the power roller, i.e., the trunnion axis, at the identical stroke. The trunnion with the power roller is allowed to pivotally move about the pivot axis due to component of force of the rotation of the input disk. A combined joint is mounted to each of the upper and lower end portions of the trunnion in order to allow the offset and pivot motions of the trunnion.
In a case where a central portion of each of the upper and lower links is pivotally supported to the transmission case by means of a pin, the upper and lower links will not be displaceable in all directions lying in a plane perpendicular to an axis of the pin. In this condition, when one of two pairs of trunnions, namely, the front trunnions or the rear trunnions, interfere with the upper and lower links during the offset motion thereof, the other of the two pairs of the trunnions undergo the interference force in the direction of the pivot axis via the pins acting as a fulcrum. Distribution of the torque to the power rollers on the front and rear trunnions will be deteriorated so that slippage will occur between the power rollers and the input and output disks.
U.S. Patent Application Publication No. U.S. 2001/0016534 A1 (corresponding to Japanese Patent Application First Publication No. 2001-182793) discloses a toroidal CVT including upper and lower links which are swingably moveable upward and downward along trunnion axes. This related art has also proposed the structure in which the upper link and the lower link are displaceable within a limited region along the trunnion axes in order to eliminate interference of the upper and lower links with components other than the trunnions. The limited region is defined between a stop mounted to an axial end portion of each of the trunnions, and a step portion formed on the trunnion. The stop restricts displacement of each of the upper and lower links in a direction in which each of the upper link and the lower link removes from the trunnions, while the step portion restricts displacement of each of the upper and lower links in the opposite direction.